The invention relates to a sensing head for the three-dimensional sensing of workpieces. The sensing head includes an essentially cylindrical housing, a transmission member, which is mounted movably therein in the axial direction and interacts with a primary element. A sensing pin which projects from the housing is seated against a bearing body shaped as a spherical segment. The transmission member is moved by pivoting the sensing pin about the spherical center-point and by the thus-effected inclination of the flat surface. Sensing heads of this kind are used in measuring machines or, mounted instead of a tool onto the tool carrier, in numerically controlled machine tools for the creation of measured values. In this case, the primary element which is used can have a purely switching function or a function measuring the linear path of the transmission member. It is a matter, in any event, of transforming the deflection motion of the sensing pin with maximum accuracy into a linear motion of the transmission member.
A typical example of a sensing head of the type defined in the introduction is described in U.S. Pat. No. 3,250,012. In this, the sensing pin is attached to the spherical side of the bearing body. The bearing body is received, with its spherical shape, by an annular step bearing, which is a component part of the housing and is passed through by the sensing pin. With the flat side, more precisely with the annular rim of the surface, the bearing body bears against the flat, radial front face of a displaceable sleeve serving as a transmission member. The sleeve is acted upon by a spring which thus, on the one side, holds the bearing body in its step bearing and, as a result of the mutual bearing contact of the two flat surfaces, returns the sensing pin into its rest position coaxial to the longitudinal axis of the housing.